RARE-EARTH COBALT PERMANENT-MAGNETS

This paper reviews the historical background and the development of rare earth-cobalt-based permanent magnets from basic science studies on rare earth-transition metal alloys in the 1960's to today's broad spectrum of commercial magnet types and their applications. It puts the RE-Co magnets in perspective relative to older magnet types and also traces the path to the subsequent development of the related Nd-Fe-B magnets. The treatment is qualitative, with emphasis on the relationship between fundamental properties of the compounds and the interaction between microstructure and magnetic domain walls that makes high coercivity and the exceptional hard magnetic properties of the rare-earth magnets possible. The various kinds of RE-Co magnets in production and use today, some of their engineering properties, and economic aspects governing their applicability, cost and availability are also discussed. Many references provide a guide to the special literature regarding the physics, metallurgy, manufacture, product selection and properties of rare earth-cobalt magnets.